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Sent this letter with lots of questions to DECC today. I wasn't aware of the this problem until this week. Perhaps engineers more familiar with this may wish to comment. I have invited DECC to speak to the IET on this connected set of issues.

James Arathoon

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Dear DECC,

We are having to go through the process of having to have our gas supply pipes upgraded now that we have had a new condensing boiler installed to replace our old back boiler. The gas engineers tell me that this is quite a common occurrence. (Our original pipe was between 10 to 15 meters of 20mm bore with a short section of 16mm bore to turn the corner into the house. There was a 10mm steel insert linking the short 16mm section to the 20mm pipe) This is currently being upgraded to a 25 mm bore pipe to the meter with a short 2 ft 20 mm section to the gas main. If this is not enough we will have to have our spur of the gas main renewed in 25 mm as well. If this doesn't work we will need an even larger bore spur of the gas main. Our gas main pressure before the regulator is around 23 mbar above atmospheric.

We have just substantially upgraded the insulation on our solid walled 1930's semi-detached house and are using a mid-sized boiler in the Worcester-Bosh combi range.

Have you carried out statistical surveys to tell you what proportion of new condensing boiler upgrades require the bores of the gas supply pipes that run from the gas main to the house to be enlarged?

If you have, can you tell me what this proportion is? Also in cases where this happens can you tell me the average cost per condensing boiler install of doing this work. Are condensing boilers failing in significant numbers because of gas supply pressure problems?

What is the statutory minimum gas main pressure? Does the statutory minimum gas main pressure now need to be increased to cater for these new condensing boilers? and would this help avoid the need to upgrade gas connection infrastructure when new condensing boilers are fitted? Could changes be made to the design of condensing boilers that would help make them work better with existing gas supply infrastructure?

If we organise boiler upgrades in a different way can we spend more public money upgrading insulation and less upgrading gas service infrastructure?

Who is the systems/integration engineering expert in government who has thought through all these multi-faceted issues? Would they be willing to come to an IET engineering event to explain the governments thinking on such complex interconnecting engineering problems and how they are best solved? Do you have enough multi-disciplinary systems and integration engineers at DECC?

Who is the systems/integration engineering expert in government who has thought through all these multi-faceted issues?

Thanks for that James - I haven't stopped laughing for ten minutes after splurting tea all over my keyboard when I read it.

Low pressure gas has a satutory limit of 75mbar in the main and is usually around 30 - 50mbar

The minimum pressure of the main cannot be below 12.5mbar. Usually the meter governor is set to 21mbar.Your pipework design will be limited to 21mbar max

A lot of modern boilers will be sensitive to low gas pressure however the downstream installation from the meter should be limited to 1mbar drop and most condensing boilers only need about 18 - 20mbar anyway.

With the original gas pipework with the gas fire, gas cooker and condensing boiler in test mode we were seeing a drop to 13 mBar. The 21 mBar Regulator was found to be working fine. Therefore we were seeing a 10 mBar drop from mains pressure.

Apparently back-boilers work fine with such an arrangement, but condensing boilers can cut out.

With the old pipe arrangement and a 10 mBar drop we would end up with a 2.5 millbar feed at the statutory minimum. No doubt this would happen in the depths of winter just as we needed our boiler most.

I made a previous comment in a letter about the lack of engineering expertise at DECC and saw a job advert for engineers a couple of weeks later. This may have been just a coincidence, but my life is so full of these types of coincidence, that I like to believe that in at least some of these instances my comments have the necessary effect.

I'm remembering some stuff because we had a problem when our new boiler was put in.

At your meter, the pressure should be 20mbar or so, and not much less. If the pressure at the meter reads 20mbar but the pressure at your boiler is much lower, then its your problem to improve your home piping to 22mm etc.

We had the problem that the pressure at our boiler was <<20mbar when the new boiler was cranking hard. Immediately the Transco guy measured this (it was 2mbar if I remember correctly!), he turned off our gas supply and put in the emergency call. Transco came the next day (we were prioritised due to very young children at the time). They didn't need to increase any pipe diameter, but the old pipe (street to our meter) was clogged with 80 years of "gunge". They blew it out and inserted a new plastic pipe inside (thats quite a trick, seeing as it crossed the entire road underground and then did a 90 degree bend in our solum).

Because is was on the "grid" side of the meter, it didn't cost us a penny. Don't ask me about Transco's costs though. In fairness, this would have been a problem with any boiler, but the most likely time to spot it is when your new combi goes in. Telltale signs are the cooking gas hob burners going out when the boiler kicks in. Our combi boiler seemed to be quite happy on 2mbar by the way, although the gas engineer was astonished it was working!

I suspect that the gas main pressure does NOT need to be increased above 20mbar since the "peaky" combi usage per household will tend to aggregate out over the neighbourhood. Also, there is a tremendous volume of gas in the mains and it provides a nice storage reserve in itself. I believe pressure is deliberately increased a tad by Transco when high demand is forecast for this reason, and its called "linepack" if I am not mistaken?

I was only asking whether the statutory lower limit of 12.5 mBar needs to be increased, if large numbers of combi boilers speced for in the region of 20 mBar are installed. If you want to make use of the 21 mBar meter regulator to improve reliability it might seem best to maintain the gas main pressure slightly above 21 mBar at minimum. I am not a gas engineer so I don't know the infrastucture costs of guaranteeing this level as a statutory minimum to enhance the reliability of condensing boilers.

I am also questioning the aggregate infrastructure costs of changing to combi boilers because we all pay for this in our bills - and this is a sort of hidden green deal system in a way.

If the combi boiler costs approx £1000 and the gas infrastucture costs are some multiple of this, then this is ok if this is a rare occurance. However if this is happening to a large number of people (and indications are that it is), then the aggregate cost to the public bill payer could really start to escallate as more and more people change over to condensing boilers.

1. Combi boilers work their hardest when heating water, so insulating houses only has a partial effect on derating the maximum power output of the boiler. Would need to add electrical top up heating for the hot water to minimise the power output of the gas boiler, to the size needed for heating a well insulated house.

As combi boilers are at their least efficient in heating hot water, this may be worth considering. There may be a slight energy cost penalty associated with such a hybrid system and this would need to be evaluated. There may be no overall cost advantage here if gas supply upgrades are still needed even for the derated condensing boilers.

2. The old statutory minimum gas pressure of 12.5 mBar now seems effectively defunct. It seems that the grid operator cannot safely run the gas main pressure that low now that condensing boilers attached to the grid.

3. Our Baxi gas fire can still be used if the back-boiler is decommissioned properly according to the manufacturers instructions. Apparently some firms are advising that these have to be ripped out even if they are in good condition and the manufacturer says that they can be used in this way. This may be sometimes be leading to unnecessary extra costs to the consumer.

4. Ofgem have confirmed to me that they do not collect statistics on the percentage and cost of gas supply upgrades needed when new combi-boilers are fitted.

Having written to DECC on this subject, they were unable to answer my questions and rather than letting me know directly, transferred my email to the Department for Communities and Local Government, which has just sent me a letter.

The Department for Communities and Local Government have confirmed to me, that they do not hold the statistics on the knock on infrstructure upgrade costs I am after.

Apparently the Heating and Hot Water Information Council (HHIC) do collect replacement boiler statisics, but not details of knock on infrastructure upgrade costs.